Conventionally images from Image Intensifier (II) are circular as the geometry of Image Intensifier (II) is circular. Hence the image formed by imager is circular and rotation is achieved either by mechanically rotating a charge coupled device that is coupled to the image intensifier or by digitally rotating the images in software.
On the other hand, a square Flat Panel Detector (FPD) when rotated digitally poses problems in displaying the rotated image. Since the diagonal of a square is of length √2*L (L is the side of the square), in order to display the image from square flat panel detector a display size capable of accommodating diagonal of the square is to be provided. Alternatively, in order to display the entire image one needs to shrink or crop the rotated image.
However, regulations in medical industry constrain cropping images that are obtained by exposure to radiation. This disadvantage leaves the user with two options, either shrinking the rotated image prior to displaying or restricting the exposure to a centered circle (by applying a circular mask). The limitation in using these methods is shrinking the displayed image results in variation of the image size along with the angle of rotation thereby causing degradation of obtained image quality. Further, applying a circular mask impacts effective area usage. The effective area usage of the flat panel detector reduces significantly (by 21.5 percent) with a circular mask.
Some of the prior art methods suggest achieving image rotation either by rotating flat panel detector mechanically by 360° or by performing digital image rotation. One of the challenges in such methods is performing a 360° mechanical rotation of the flat panel detector. Further, digital rotation too has its impact on Image Quality (Interpolation loss/artifacts, cropping of image corners or shrinking the image size) as explained above.
Using such methods for image processing and display, the user is forced to choose between image size and field of view.
Hence there exists a need for an efficient and improved method of processing and displaying an image that overcomes the drawbacks of digital rotation with square images, and which also maintains the image size while providing increased field of view.